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UC San Diego Engineers Try To Redesign Heart Pump

Reported by Nicholas Mcvicker

Mechanical engineers at UC San Diego are trying to come up with a better designed heart pump.

— The Berlin Heart is an external pump for children who have a malfunctioning heart. It buys kids some time for either their heart to recover, or until a donated organ is found.

Photo by Kenny Goldberg

Karly Nuttal was born with an enlarged heart in 2007. Surgeons hooked her up to a Berlin Heart pump when she was just two weeks old. After 15 days, her own heart was well enough to function on its own.

The device can be a lifesaver, but it has some serious flaws. Mechanical engineers at UC San Diego are trying to come up with a better design.

When Karly Nuttal was born in Tucson in 2007, her heart was barely functioning.

Doctors pulled her parents aside and gave them the grim news.

"They said, you know, that her heart was in such bad shape, that they didn’t expect her to live through the night," Karly's mom, Stacy, recalled.

Somehow Karly survived that night. For the next two weeks, it was touch and go.

Then, Karly got a Berlin Heart. It’s the only FDA-approved cardiac pump for young children. Doctors said it would hopefully keep Karly alive until they could find a donated heart.

"So that was the plan, is get the Berlin Heart on, let her grow and get bigger, and then hopefully a heart would become available for a heart transplant," Stacy Nuttal said.

After five days, doctors dialed back the device. They wanted to see how Karly’s own heart would respond.

"After 15 days, they were able to dial it all the way down to zero, and her heart was doing the work it needed to do," Nuttal said, as she choked back tears. "So they were able to take the Berlin Heart off, and now she just has her own heart, and we are just very grateful."

The Berlin Heart is often the only thing standing between life and death for children with damaged hearts. But the device itself is risky. It causes blood clots, which lead to strokes in at least one out of every four kids.

UC San Diego’s Alison Marsden hopes to change that. She’s an assistant professor of mechanical and aerospace engineering. Marsden became interested in medical devices during her post-doctoral training at Stanford.

"I think the patterns of blood flow in surgeries and devices are really interesting from an engineering point of view," Marsden explained. "But also, I enjoy working on those problems, because of their immediate application to sort of human problems and patient care."

The Berlin Heart is a palm-sized device with two tubes at one end and one tube at the other.

"So this device is made up of two chambers: there’s a blood chamber on the top, there’s an air chamber down here, and there’s a rather thin membrane that divides the two chambers," Marsden said, as she held the device. "And so when the bottom chamber is pressurized, the membrane goes up and down. But its motion is non-linear, so, meaning that it buckles in a complex pattern."

Marsden’s been working on a computer simulation of the Berlin Heart.

It’s an enormous challenge. There’s the complex interplay between blood, air and the membrane. And one has to calculate three components of velocity and pressure at each of more than 2 million points inside the device.

UC San Diego structural engineer Yuri Bazilevs said you can't just pull some software off the shelf to work out all of the calculations.

"The current sort of state-of-the-art in commercial codes is that such problems are, I would say, nearly impossible or impossible to do," Basilevs explained.

Bazilevs is an expert in complex mathematics and computer science. He shares Marsden’s fascination with medical devices. Bazilves has used some formulas he devised and some super computers on campus to help develop the simulation.

"So basically, I’m taking the methods I’ve developed for cardiovascular blood flow, as well as things like surface ships or wind turbines, and we’re applying it to this very interesting and challenging problem," he said.

After working on it for two years, Marsden and Bazilevs have come up with what they think is a viable computer simulation of the Berlin Heart.

Marsden pointed to her computer screen as the simulation flashed into action.

"Basically, colors indicate how fast the flow is moving. And on the bottom here is the air chamber, on the top is the blood chamber, and the motion that you’re seeing is this membrane that goes up and down," she said. "And you can see that is has a very complex buckling motion, which is something that was quite challenging to capture in the simulation.”

Marsden says it’s a good start. But they’ll need to develop a more sophisticated model to figure out how blood clots form inside the device. Then they can suggest some design changes.

Since its introduction, an estimated 1,000 children worldwide have used the Berlin Heart.


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